Cellular telephone systems and Internet protocol systems (e.g., Voice-over-IP, instant messaging) provide mobility to users allowing them to remain “connected” on at least one network as they travel over a wide geographic area. An approach has been proposed to coordinate cellular telephone and IP-based telephony such that information to a cellular telephone user can be directed to an IP-based telephone when the user can receive calls as such a telephone, and calls can be handed off between an IP-based connection and a cellular telephone based connection.
In addition, mobile telephone units are becoming available that include radio interfaces to both cellular telephone radio networks, and wireless local area networks. For example, a user can use telephone services over the cellular network while accessing data services over the wireless local area network.